Humans sleep to maintain health and well being. Certain sleep disorders may interfere with the ability to obtain a proper and healthy amount of sleep. Other diseases may also interfere with the ability to obtain sleep, or may be related to one or more types of sleep disorders. Similarly, certain sleep disorders may exist as co-morbidities with other health disorders. Furthermore, certain physiological variables may be affected by sleep or by circadian rhythms.
Sleep includes rapid eye movement (REM) sleep and non-REM (NREM or non-REM) sleep. Typically, sleep onset is NREM. Such NREM sleep can be conceptualized as including four stages, ranging from light to deep sleep. A NREM sleeping person typically cycles through these four stages of sleep approximately every 90 minutes. NREM sleep is typically followed by REM sleep, the most active stage of sleep when dreaming often occurs. During REM sleep, the eyes may move back and forth beneath the eyelids and muscles may become immobile.
Diagnosing sleep disorders, such as sleep apnea, typically involves conducting a sleep study in a hospital sleep laboratory. For example, congestive heart failure (CHF or HF) and other cardiac patients often exhibit sleep disorders as a co-morbidity. As a result, cardiologists routinely rely on hospital sleep laboratories to conduct testing on their patients. However, hospital sleep laboratory studies are expensive. Moreover, such studies require the patient to spend time at the sleep lab while the testing is conducted. In sum, sleep determination has many important and clinically useful applications.